Surface wave ambiguity analyzer

ABSTRACT

A surface-wave ambiguity analyzer comprising a substrate, capable of propagating an acoustic surface wave on its surface, and a transmitting electroacoustic transducer, disposed upon the substrate, having a perimeter substantially in the shape of a trapezoid whose base is parallel to the direction of surface wave propagation. The transmitting transducer comprises a pair of sets of interdigited electrodes, the configuration of the electrodes conforming in shape to the graphs of a set of regular functions which do not cross or otherwise touch each other, a top bus bar, parallel to the base of the trapezoid, to which one of the sets of electrodes is connected, and a bottom bus bar, forming the base of the trapezoid, to which the other set of electrodes of the pair of sets is connected, the top and bottom bus bars being connectable to an electrical signal source. Two absorbers, one on each end of the substrate, are disposed perpendicularly to the base of the trapezoid, for absorbing unwanted acoustic reflections. The ambiguity analyzer may further comprise at least one acousto-electric receiving transducer, disposed at one end of the substrate between the transmitting transducer and one of the absorbers, whose electrodes are disposed perpendicularly to the direction of propagation of the acoustic wave.

United States Patent 91 Whitehouse 1 Apr. 17, 1973 [54] SURFACE WAVEAMBIGUITY ANALYZER [75] Inventor: Harper John Whitehouse, San

Diego, Calif.

[73] Assignee: The United States of America as represented by theSecretary of the Navy [22] Filed: Nov. 24, 1971 [21] Appl. No.: 201,693

[52] US. Cl. ..l81/.5 AP, 181/.5 R, 333/30, 73/170, 324/80 [51] Int. Cl..H03h 7/30, GOlr 23/00 [58] Field of Search ..333/30, 72; 181/.5 R, .5AP; 73/170; 324/80 [56] References Cited UNITED STATES PATENTS 3,582,8386/1971 DeVries .333/30 3,573,673 4/1971 DeVries ..333/30 PrimaryExaminerBenjamin A. Borchelt Assistant Examiner-J. V. DoramusAttorney-Richard S. Sciascia et al.

[5 7] ABSTRACT A surface-wave ambiguity analyzer comprising a substrate,capable of propagating an acoustic surface wave on its surface, and atransmitting electroacoustic transducer, disposed upon the substrate,having a perimeter substantially in the shape of a trapezoid whose baseis parallel to the direction of surface wave propagation. Thetransmitting transducer comprises a pair of sets of interdigitedelectrodes, the configuration of the electrodes conforming in shape tothe graphs of a set of regular functions which do not cross or otherwisetouch each other, a top bus bar, parallel to the base of the trapezoid,to which one of the sets of electrodes is connected, and a bottom busbar, forming the base of the trapezoid, to which the other set ofelectrodes of the pair of sets is connected, the top and bottom bus barsbeing connectable to an electrical signal source. Two absorbers, one oneach end of the substrate, are disposed perpendicularly to the base ofthe trapezoid, for absorbing unwanted acoustic reflections. Theambiguity analyzer may further comprise at least one acousto-electricreceiving transducer, disposed at one end of the substrate between thetransmitting transducer and one of the absorbers, whose electrodes aredisposed perpendicularly to the direction of propagation of the acousticwave.

9 Claims, 4 Drawing Figures I/vPar 675mm 32 (J's/caps [@5455 MrsAwa/aalry A l/41.7259.

SURFACE WAVE AMBIGUITY ANALYZER STATEMENT OF GOVERNMENT INTEREST Theinvention described herein may be manufactured and used by or for theGovernment of the United I BACKGROUND OF THE INVENTION This inventionrelates to a surface wave device, preferably of the field-delineatedtype, capable of providing a simultaneous evaluation of analysis ofexact wideband signal ambiguity, in compression and delay, by means of asingle surface wave structure. A fielddelineated transducer includes athird set of interdigitated, and interconnected, electrodes locatedbetween the interdigitations of the regular pair of electrodes, forcontrolling, or delineating, the field or direction of the acousticsurface wave produced by the transducer. The two-dimensional surfacedisturbance produced on the surface wave ambiguity analyzer correspondsto the true ambiguity surface of the signal and the electrode pattern,and this pattern, and therefore the ambiguity in the modified dopplersignal, may be detected in various ways.

The ambiguity analyzer analyzes ambiguity by providing the ambiguity ina two-dimensional displacement of the surface of the crystal substrate.

Basically, wideband doppler ambiguity is analogous to narrow-banddoppler ambiguity in the sense that in each of them one cannotsimultaneously specify the range behavior and the doppler behavior. Thedetails of the difference are: For narrow-band doppler, afrequency-shift of the carrier is used, whereas in wideband doppler anactual time expansion or contraction of one of the signal waveforms isused.

The range of doppler-which may be detected, that is, the differencebetween the highest doppler frequency and the lowest doppler frequency,is determined, on the ambiguity analyzer, by the difference between thewidths of the top and bottom parts of the transmitting transducer.Generally, the transmitting transducer would be so configured that themedian, or reference, frequency would match the frequency as determinedby the spacing of the electrodes, and the material of the substrate, ata median horizontal distance between the top and bottom bus-bars.

However, these frequencies cannot be observed directly. Rather they areobserved in the autocorrelation function, which is the Fourier transformof the spectrum. So, what is actually observed are signals in the timedomain rather than in the frequency domain. I There exists on thecrystal a complete two-dimensional range-doppler distribution, to whichmay be applied well known readout techniques in order to be able todetermine the required output.

A specific doppler may be determined in any of various prior artmethods. A column of receiving transducers consisting of parallelelectrodes may be placed at the receiving end, between the transmittingtransducer and one of the absorbers, to pick up individual voltagetrains,which are functions of the various dopplers present in the inputtrain.

Instead of piezoelectric output transducers, optical reflectors,stationary or scanned, may be used. A light beam can be shined on thereflectors, with the reflected light received by an array ofphotodetectors, the amount of reflected light being a function of thedoppler frequency. Frustrated internal reflection of light may be used.

A moving conductor may be used, with the complete ambiguity analyzerplaced in a magnetic field. This also is a prior art method.

If either an array of electrical outputs or a two dimensional outputsuch as a scanning light beam or a scanning electron beam is used, aTV-like raster will be generated which is the true ambiguity function ofthe signal represented by the electrode structure or the cross ambiguityfunction of the signal and pattern if these are different functions.

For general information about the propagation of acoustic signals onsurface wave devices, as well as theoretical information about spectralanalysis by surface wave devices, using parallel-electrode transducershowever, reference is directed to US. Pat. No. 3,548,306, by the sameinventor, which issued on Dec. 15, 1970. I

SUMMARY OF THE INVENTION This invention relates to a surface wavedevice, having interdigitated electrodes, of the field-delineated type,capable of providing a simultaneous evaluation or analysis of exactwideband doppler ambiguity by means of a single surface wave structure.The doppler ambiguity refers to the ambiguity in determining both theamount of delay and the amount of doppler, or in the range and rangerate.

A field-delineated transducer, used in the transmitting transducer,includes a third set of interdigitated electrodes, located between theinterdigitations of the conventional pair of electrodes, forcontrolling, or delineating, the field or direction of the acousticsurface wave produced by the transducer.

In a very general sense, the ambiguity analyzer performs thesimultaneous cross correlation of one parameter, the given input signal(electrical),with a second parameter, the time-scaled versions of asecond signal determined by the reference signal electrodes.

a. If the input signal is one of the reference signals, the ambiguityanalyzer computes the ambiguity function of that signal, the variablesbeing delay and time scaling.

b. If the input signal is a superposition of delayed and time-scaledreplicas of the reference function, it computes the radar or sonarmapping of the received echos. The variables are range and doppler orrange rate.

c. If the input signal is a mismatched version of the referencefunction, intentionally introduced at transmission, then the mappingdescribed may sometimes be achieved with better fidelity.

d. If the signal is general and the reference function a sinusoid, thenthe device acts as a spectrum analyzer.

OBJECTS OF THE INVENTION An object of the invention is to provide asmall, compact, surface wave device which can analyze input signalssimultaneously for doppler and delay.

Another object of the invention is to provide a surface wave devicewhich can determine the frequency or frequencies which comprise theinput signal.

, Still another object of the invention is to provide a surface wavedevice which, by using coded transducers,

can analyze for doppler and delay while amplifying the signal traversingthe substrate.

Other objects, advantages, and novel features of "the invention willbecome apparent from the following detailed description of theinvention, when considered in conjunction with the accompanying drawingswherein:

I BRIEF-DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic view of asurface wave ambiguity'analyzer using a pair of sets of uncodedtransducers for the transmitting transducer.

FIG. 2 is a diagrammatic view of a coded surface .waveanalyzer whichincludes. a third set, afieldfor the transmitting transbiguity analyzerhaving electrodes curved according to 1 a set of regular functions.

I DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, thisfigure shows a surface a wave ambiguity analyzer comprisinga substrate12, capable of propagating an acoustic surface wave onxits surface, thedirection of propagation indicated by double-headed arrow 14. 1

A transmitting electroa'coustic transducer '20,

disposed uponthe substrate" 12, has a perimeter substantially in theshape of a trapezoid, whose base 26 is parallel to the direction ofsurface wave propagation 14. The transmitting transducer 20 comprises apair of vsetsofinterdigitated electrodes, 22 and 24, the conzoid, towhichone of the sets of electrodes 24 is con- I nected, while a bottombus bar 26 forms the base of the trapezoid, to which theother set ofelectrodes 22 of the pair of sets is connected. The top and bottom busbars,28 and 26,are connectable to'an electrical signal source by meansof input terminals 32. Two absorbers, 34L and 34R, one on each end ofthe substrate 12, are disposed perpendicularly to the base 26 of thetrapezoid, for absorbing unwanted acoustic relfections. f I

The ambiguity analyzer 10 may further comprise at least oneacousto-electric receiving transducer 30, disposed at one end of thesubstrate 12 between the transmitting transducer 20 and one of theabsorbers 34R, its electrodes being disposed perpendicularly to'disposed on the substrate. Frustrated internal reflecmitting transducer20 and used it to generate-the signal,

i.e., it is a codedsignal whose code is that given by the polarityreversals'and whose duration is that halfway through the transmittingtransducer, at line 16.

The waves which are present at' various horizontal levels on theambiguity analyzer are not true sine waves, but rather are the resultobtained by convolving the input signal with each particular horizontalslice of thetransducer 20. They in turn are the cross-correlation at aparticular doppler error. That is, at the top of the transducer 120,near top bus bar '28, the nominal signal correlated with a compressedversion isobtained. At the center 16, a nominal signal correlated withitself is obtained. At the bottom of the surface wave analyzer, near thebus bar 26, a signal is obtained which results from the correlation withthe expanded version of the signal.

In effect, generally the whole doppler spectrum may becovered. The ratioof the highest doppler frequency to the lowest doppler frequency coveredis a function I of the width of the top of the transmitting transducer20 to the. width of the bottom of the transmitting transducer. I V Y Thefrequency that is transmitted by thetrapezoidal transducer 20 is anarrow-band frequency compared to the bandwidth of any of the receivingtransducers 30. If the receiving transducer 30 had a narrow-bandresponse, the ambiguity ,functioriywhich is. being mea sured maybedistorted by the filtering actionfof the output transducer 20. i

It is because of the comparatively great bandwidth of thesingle-fingered receiving transducers 30 that permits making all of themof the same electrode spacing, thus making them easier to fabricate.However, par ticularly for use as a spectrometer, it would beadvantageous to make the spacing of the electrodes of each receivingtransducer 30 the same as that-of the corresponding horizontal sectionof the transmitting transducer, and this is shown in FIG. 4. A singleshielded finger ischosen' forjthe receiving transducers30 becausethistype of transducer has a very high bandwidth, so high that evenif itsfinger spacing does not match thatof the finger spacing of thecorresponding horizontal section in the transmitting transducer 20, thereceiving transducer will accomplish its purpose. 1

With respect to the dimensions of the interdigitations themselves, thewidth of each electrode, for example,

electrodes 22 or 24, should be equal to the width of the the directionof propagation of the acousticwave,

designated by double-headed arrow 14.

Only the transmitting transducer. 20 need be disposed on the crystallinesubstrate .12, using'the piezoelectric effect. The output may beobtained by other means than using a piezoelectric transducer alsospacebetween two adjacent electrodes. For 'clarityof representation, inthe various figuresthe electrodes are shown much thinner than thisratio. If one interdigitation is considered to consist'of one up" lineand two down" lines as'in receiving transducers 30, the width oftheinterdigitation should be equal to one wavelength acts as a shieldfor the other. However, when the electrodes are coded, this condition isno longer true, and a third, shielding, electrode must be introducedbetween the first pair of sets 22 and 24.

Accordingly, FIG. 2 shows a coded ambiguity analyzer 40 wherein thetransmitting transducer 42 further comprises, besides the regular pairof electrodes 44 and 46, a third set of electrodes, a fielddelineating,interconnected, set 48, disposed between the regular pair.

In FIG. 2 the output waveforms are not shown, but they would notgenerally be even approximately sinusoidal, inasmuch as the transmittingtransducer 42 is coded. The specific shape of the output waveforms, ofcourse,would depend on the specific coding of the transmittingtransducer 42, the specific coding in this figure being 1 l l 0.

The ratio of the finger spacing at the bottom of the trapezoid to thefinger spacing at the top of the trapezoid could be as high as two toone for wideband ambiguity problems, but could be much less than thisfor specific applications, such as radar.

The two-headed arrow 14 indicates that a surface wave travels in bothhorizontal directions, to the left and to the right, toward the twoabsorbers, 34L and 34R. The acoustic wave going to the left iscompletely useless, and it is desirable that it be completely absorbedby left absorber 34L. The surface wave moving to the right is the usefulwave, and, it is desirable that all of it be intercepted by thereceiving electrodes 30 rather than right absorber 34R. In the absenceof the right absorber 34R, any surface wave which passed by thedetecting means, such as the column of receiving transducers 30, wouldbe reflected off the right edge of the substrate 12, and then travel ina leftward direction, to interfere with the oncoming surface wavetraveling to the right.

The individual electrodes of each of the sets of electrodes of thetransmitting transducer need not have a linear shape, as shown in FIGS.1 and 2, but may have discrete offsets 52, 53, 54 and 55, in the form ofa staircase function, as shown by the transmitting transducer 51 of theambiguity analyzer 50 shown in FIG. 3. In this embodiment, there wouldgenerally be between and 30 channels, with perhaps an upper limit of 100channels, rather than only the four channels shown.

In the embodiment shown in FIG. 4, the electrodes 74 are perpendicularto the bus bar 78 where they join it, and then curve away from theperpendicular as their distance from the bus bar increases, in aquadratic manner, for example, if desired. The exact curvature ofelectrodes 72 and 74 would depend on the range of frequencies expectedin the input signal, for example, whether the input signal hadacceleration components in it or not.

The embodiments shown in the various figures may be used for spectralanalysis in the following manner. The wavelength and therefore frequencydetermined by a particular section of the transmitting transducer is afunction of the spacing of the electrodes in that particular section, aswell as the material of the substrate. The closer the spacing, thehigher the frequency determined by these two parameters.

For improved operation as a spectrometer, the spacing of the outputelectrodes 80 at a specific horizontal distance from the base 76 of thetransmitting transducer 70 should be the same as the spacing of theelectrodes of the transmitting transducer at that same height. This typeof configuration is shown in FIG. 4. Output signals 82 may be obtainedat each of the output terminals 84, the magnitude of the signal at aparticular output transducer 80 depending upon how closely the frequencydetermined by its electrode spacing matches the frequency of the inputsignal.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within There would be one receiving transducer 30 foreach 7 offset in the transmitting transducer 51.

FIG. 4 shows yet another embodiment of an ambiguity analyzer wherein thepair of sets of electrodes 72 and 74 are curved, in this figure,quadratically and symmetrically about the center electrode 74M.

In a more general embodiment, the spacing need not be symmetric about acenter electrode, for example, for processing chirps and similarsignals.

the scope of the appended claims the invention may be practicedotherwise than as specifically described.

What is claimed is:

l. A surface-wave ambiguity analyzer comprising:

a substrate, capable of propagating an acoustic surface wave on itssurface;

a transmitting electroacoustic transducer, disposed upon the substrate,having a perimeter substantially in the shape of a trapezoid whose baseis parallel to the direction of surface wave propagation, comprising:

a pair of sets of interdigitated electrodes, the configuration of theelectrodes conforming in shape to the graphs of a set of regularfunctions which do not cross or otherwise touch each other;

a top bus bar, parallel to the base of the trapezoid,

to which one of the sets of electrodes is connected;

a bottom bus bar, forming the base of the trapezoid, to which the otherset of electrodes of the pair of sets is connected;

the top and bottom bus bars being connectable to an electrical signalsource;

two absorbers, one on each end of the substrate,

disposed perpendic-ularly to the base of the trapezoid, for absorbingunwanted acoustic reflections and;

at least two acoustic-electric receiving transducers, disposed at oneend of the substrate between the transmitting transducer and one of theabsorbers, whose electrodes are disposed perpendicularly to thedirection of propagation of the acoustic wave.

2. The ambiguity analyzer according to claim 1,

wherein the pair of sets of electrodes are uncoded.

3. The ambiguity analyzer according to claim 2,

wherein the pair of sets' of electrodes are coded.

4. The ambiguity analyzer according to claim 3, 7. The ambiguityanalyzer according to claim 4, wherein the transmitting transducerfurther comprises h i a third Set of electrodes, a field'delmeatingintercom the individual electrodes of each of the three sets of nected,set disposed between the pair of sets of electrodes, and conforming inshape to the same set of regular functions as the pair of sets ofelectrodes.

5. The ambiguity analyzer according to claim 4, wherein the set ofregular functions are a'set of linear functions. 10

6. The ambiguity analyzer according to claim 4, wherein the set ofregular functions are a set of quadratic functions. I i

electrodes of the transmitting transducer have the shape of a staircasefunction. 8. The ambiguity analyzer according to claim 4, wherein thetwo lateral sides of the trapezoid are equal.

9. The ambiguity analyzer according to claim 5, wherein the two lateralsides of the trapezoid are equal.

1. A surface-wave ambiguity analyzer comprising: a substrate, capable ofpropagating an acoustic surface wave on its surface; a transmittingelectroacoustic transducer, disposed upon the substrate, having aperimeter substantially in the shape of a trapezoid whose base isparallel to the direction of surface wave propagation, comprising: apair of sets oF interdigitated electrodes, the configuration of theelectrodes conforming in shape to the graphs of a set of regularfunctions which do not cross or otherwise touch each other; a top busbar, parallel to the base of the trapezoid, to which one of the sets ofelectrodes is connected; a bottom bus bar, forming the base of thetrapezoid, to which the other set of electrodes of the pair of sets isconnected; the top and bottom bus bars being connectable to anelectrical signal source; two absorbers, one on each end of thesubstrate, disposed perpendic-ularly to the base of the trapezoid, forabsorbing unwanted acoustic reflections and; at least twoacoustic-electric receiving transducers, disposed at one end of thesubstrate between the transmitting transducer and one of the absorbers,whose electrodes are disposed perpendicularly to the direction ofpropagation of the acoustic wave.
 2. The ambiguity analyzer according toclaim 1, wherein the pair of sets of electrodes are uncoded.
 3. Theambiguity analyzer according to claim 2, wherein the pair of sets ofelectrodes are coded.
 4. The ambiguity analyzer according to claim 3,wherein the transmitting transducer further comprises a third set ofelectrodes, a field-delineating, interconnected, set disposed betweenthe pair of sets of electrodes, and conforming in shape to the same setof regular functions as the pair of sets of electrodes.
 5. The ambiguityanalyzer according to claim 4, wherein the set of regular functions area set of linear functions.
 6. The ambiguity analyzer according to claim4, wherein the set of regular functions are a set of quadraticfunctions.
 7. The ambiguity analyzer according to claim 4, wherein theindividual electrodes of each of the three sets of electrodes of thetransmitting transducer have the shape of a staircase function.
 8. Theambiguity analyzer according to claim 4, wherein the two lateral sidesof the trapezoid are equal.
 9. The ambiguity analyzer according to claim5, wherein the two lateral sides of the trapezoid are equal.